Rising Rates of Colorectal Cancer in Young Adults Linked to Bayer’s RoundUp Weedkiller

A peer-reviewed study published Apr. 21, 2026, in Nature Medicine by researchers in Spain has found that rising early-onset colorectal cancer in younger adults is linked to pesticide exposure via herbicides containing ingredients banned in other countries but still approved for use in the United States.¹

The study evaluated “epigenetic fingerprints” left in tumor DNA from environmental exposures and identified several chemical ingredients as associated risk factors, including glyphosate, the active ingredient in Bayer’s RoundUp; however, one ingredient, picloram, was identified as a previously undescribed risk factor, with the association replicated across nine independent cancer cohorts and further validated using population-based data from 94 U.S. counties over 21 years. The association held up even after adjusting for income, education, and other pesticide use.¹

Colorectal cancer has historically been a disease of older adults but in recent years has become a leading cause of death in young people, with approximately 1 in 5 diagnoses occurring in Americans 55 years old and younger. The American Cancer Society (ACS) classifies colorectal cancer (CRC) as “a major public health threat in the US, ranking as the second leading cause of cancer deaths (combined for men and women) with an estimated 55,230 deaths in 2026.” While the organization attributes declining cases among older adults to better screening, it reports CRC incidence is “rising at an alarming rate” at roughly three percent annually among people under 55.²

EPA Documented Dietary Exposure and Groundwater Contamination from Common Pesticide in 1995

Picloram was first registered as a pesticide in the U.S. in 1964. Three decades later, the U.S. Environmental Protection Agency (EPA) acknowledged in its 1995 Reregistration Eligibility Decision that people may have dietary exposure to the pesticide via grain, forage, straw, milk, eggs, and meat byproducts of cattle, goats, hogs, horses, sheep, and poultry; which the 2026 Nature Medicine study identified as the same dietary exposure pathway hypothesized to contribute to the rise in colorectal cancer diagnoses among younger patients today.^{1 3}

The study’s authors theorize that because picloram was not widely used until the mid-to-late 20th century, older patients aged 70 and older were not exposed during childhood, but younger patients were, and for a larger portion of their lives. As the study notes:

If the use of picloram in crops started in the mid and late twentieth century, then current patients with LOCRC were not exposed during their childhood, whereas cases of EOCRC were and have been for a longer part of their lives, which could explain our results.¹

The EPA itself described picloram as one of the hardest-to-contain pesticides on the market, resistant to natural breakdown and virtually guaranteed to contaminate groundwater in treated areas. The agency has continued to approve its use in the three decades since that assessment.³

According to the EPA, picloram, marketed under the brand name Tordon by Dow AgroSciences, is a restricted-use, systemic herbicide approved in the U.S. to control woody plants and deep-rooted broadleaf weeds on rangeland, pastures, forestry, and rights-of-way. It is not available for residential use and requires a certified applicator for application.³

Federal Pesticide Law Does Not Require Public Notification Before State Agency Herbicide Applications on Public Rights-of-Way

State agency officials are tasked with applying picloram-containing pesticide to control vegetation from obstructing roadways and are authorized to apply pesticides to obstructing vegetation on rural, privately owned property. Under current federal law, public notification before herbicide applications on public rights-of-way is not required. Under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), the EPA’s regulatory authority ends at product registration and labeling. What occurs between application and exposure is governed, if governed at all, by individual states.⁴

Roughly half of the states have adopted some form of prior notification requirement for pesticide applications, though most of these statutes were written around commercial lawn care operators rather than state transportation departments.⁴

For residents who wish to opt out, the burden falls entirely on them both to manage the vegetation and any associated costs. Some states offer voluntary no-spray agreements, under which landowners either maintain the right-of-way themselves or negotiate herbicide-free maintenance, oftentimes at their own expense. No federal mechanism exists to require disclosure, establish a registry, or require that residents living in the vicinity of treated corridors be informed of what chemicals were applied, at what concentrations, or how often.⁴

Glyphosate Also Among Top Pesticide Associations in County-Level Colorectal Cancer Data

Glyphosate, an active ingredient in RoundUp, also ranked among the top five most robust pesticide associations found in county-level data in the study. Despite its classification by the International Agency for Research on Cancer (IARC) as “probably carcinogenic to humans” and being the subject of thousands of personal injury lawsuits in recent years, glyphosate continues to be approved for use in the U.S.¹

Earlier in 2026, the White House extended liability protections to glyphosate, similar to the protections afforded vaccine manufacturers under the National Childhood Vaccine Injury Act of 1986, which shields them from most civil lawsuits related to injury claims.⁵

Other pesticides associated with early-onset colorectal cancer in the study include atrazine, a top-selling pesticide in the U.S. that has been banned in Europe since 2004, along with esfenvalerate, nicosulfuron, heptachlor, metolachlor, toxaphene, and polychlorinated biphenyls (PCBs). PCBs are a class of synthetic industrial chemicals whose manufacture was banned by the EPA in 1979, though exposure to existing environmental contamination persists. As the EPA documents, “PCBs do not readily break down once in the environment and can remain for long periods cycling between air, water and soil. They also can be carried long distances and have been found in snow and sea water in areas far from where they were released into the environment. As a consequence, they are found all over the world.”^{1 6}

Medical Professionals, Attorneys, Advocates Rally Outside U.S. Supreme Court Demanding Pesticide Manufacturer Accountability

Hundreds of demonstrators gathered outside of the U.S. Supreme Court in Washington D.C. on April 27, 2026 for a People vs. Poison rally, organized in opposition to Bayer receiving legal immunity against thousands of lawsuits claiming its RoundUp weedkiller causes cancer. The event was organized by Make America Healthy Again (MAHA) activists and advocates, including food safety advocate and blogger Vani Hari, known publicly as Food Babe, who spoke at the rally.⁷

“Citizens from across the country, lawyers, doctors, scientists, politicians, and farmers showed up and demanded People over Poison! Corporations poisoning Americans with toxic pesticides do NOT get legal immunity – we will not stand for it,” Hari said in a post published on her website following the event. “You cannot claim to care about health—while protecting poison. You cannot tell Americans to eat real food—while protecting the cancer-causing chemicals sprayed on it. You cannot stand with families—and side with one of the most evil corporations of the world.”⁷

On the same day demonstrators gathered outside the courthouse, the U.S. Supreme Court heard oral arguments in Monsanto v. Durnell, a case originating from a Missouri jury’s $1.25 million verdict in favor of a plaintiff who alleged decades of Roundup exposure caused his non-Hodgkin lymphoma. The ruling will determine if federal pesticide law shields manufacturers from state-level failure-to-warn claims. A ruling is expected by the end of June 2026.⁸

If you would like to receive an e-mail notice of the most recent articles published in The Vaccine Reaction each week, click here.